U.S. patent number 11,411,323 [Application Number 17/151,854] was granted by the patent office on 2022-08-09 for compact wideband dual-polarized radiating elements for base station antenna applications.
This patent grant is currently assigned to CommScope Technologies LLC. The grantee listed for this patent is CommScope Technologies LLC. Invention is credited to Peter J. Bisiules, Changfu Chen, Fan He, YueMin Li, Mohammad Vatankhah Varnoosfaderani, Bo Wu, Jian Zhang.
United States Patent |
11,411,323 |
Wu , et al. |
August 9, 2022 |
Compact wideband dual-polarized radiating elements for base station
antenna applications
Abstract
Radiating elements include a conductive patch having first and
second slots that each extend along a first axis and third and
fourth slots that each extend along a second axis that is
perpendicular to the first axis, a feed network that includes first
through fourth feed lines, each feed line crossing a respective one
of the first through fourth slots, and a conductive ring that at
least partially surrounds the periphery of the conductive patch and
that encloses each of the first through fourth slots.
Inventors: |
Wu; Bo (Suzhou, CN),
Chen; Changfu (Suzhou, CN), Li; YueMin (Suzhou,
CN), Varnoosfaderani; Mohammad Vatankhah (Richardson,
TX), Zhang; Jian (Suzhou, CN), He; Fan
(Suzhou, CN), Bisiules; Peter J. (LaGrange Park,
IL) |
Applicant: |
Name |
City |
State |
Country |
Type |
CommScope Technologies LLC |
Hickory |
NC |
US |
|
|
Assignee: |
CommScope Technologies LLC
(Hickory, NC)
|
Family
ID: |
1000006482017 |
Appl.
No.: |
17/151,854 |
Filed: |
January 19, 2021 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20210226344 A1 |
Jul 22, 2021 |
|
Foreign Application Priority Data
|
|
|
|
|
Jan 20, 2020 [CN] |
|
|
202010061865.4 |
Mar 12, 2020 [CN] |
|
|
202010168550.X |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01Q
9/0407 (20130101); H01Q 1/246 (20130101); H01Q
21/065 (20130101); H01Q 21/0075 (20130101); H01Q
13/10 (20130101) |
Current International
Class: |
H01Q
21/06 (20060101); H01Q 9/04 (20060101); H01Q
21/00 (20060101); H01Q 1/24 (20060101); H01Q
13/10 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2014062513 |
|
Apr 2014 |
|
WO |
|
2015124573 |
|
Aug 2015 |
|
WO |
|
2017178037 |
|
Oct 2017 |
|
WO |
|
2018205277 |
|
Nov 2018 |
|
WO |
|
2020151049 |
|
Jul 2020 |
|
WO |
|
Other References
"Photos of Radiating Element (Admitted Prior Art)". cited by
applicant .
"Extended European Search Report for European Application No.
21152353.5, dated Jun. 7, 2021, 9 pages". cited by
applicant.
|
Primary Examiner: Crawford; Jason
Attorney, Agent or Firm: Myers Bigel, P.A.
Claims
That which is claimed is:
1. A radiating element for a base station antenna, the radiating
element comprising: a printed circuit board that includes a
conductive patch having first and second slots that each extend
along a first axis and third and fourth slots that each extend
along a second axis that is perpendicular to the first axis; a
first coaxial cable and a second coaxial cable that each extend
from a reflector of the base station antenna to the printed circuit
board; and a conductive stub that physically and electrically
connects an outer conductor of the first coaxial cable to an outer
conductor of the second coaxial cable.
2. The radiating element of claim 1, wherein the printed circuit
board is mounted forwardly from the reflector at a distance that is
greater than one-quarter of a wavelength corresponding to the
center frequency of the operating frequency band of the radiating
element.
3. The radiating element of claim 2, wherein the conductive stub is
located at approximately one quarter of the wavelength
corresponding to the center frequency of the operating frequency
band of the radiating element from the printed circuit board.
4. The radiating element of claim 2, wherein the conductive stub is
located closer to the reflector than it is to the printed circuit
board.
5. The radiating element of claim 1, wherein the outer conductors
of the first and second coaxial cables are soldered to the printed
circuit board.
6. The radiating element of claim 1, further comprising first and
second conductive tubes that are positioned adjacent the first and
second coaxial cables.
7. The radiating element of claim 1, wherein the printed circuit
board further includes a feed network that has a first input that
is electrically connected to an inner conductor of the first
coaxial cable, a first power divider that is coupled to the first
input, first and second transmission lines that extend from the
first power divider to cross the respective first and second slots,
a second input that is electrically connected to an inner conductor
of the second coaxial cable, a second power divider that is coupled
to the second input, and third and fourth transmission lines that
extend from the second power divider to cross the respective third
and fourth slots.
8. The radiating element of claim 7, wherein the conductive patch
is implemented at least partially on a first metal layer of the
printed circuit board, wherein the feed network is implemented on a
second metal layer of the printed circuit board, wherein the second
metal layer further includes a plurality of metal pads that are
each electrically connected to the conductive patch, and wherein
each of the first through fourth slots extend to a periphery of the
conductive patch.
9. The radiating element of claim 7, wherein at least a portion of
the conductive patch is implemented on a first metal layer of the
printed circuit board, wherein the first through fourth
transmission lines comprise metal traces on a second metal layer of
the printed circuit board, and wherein each of the first through
fourth slots extend to the periphery of the conductive patch.
10. The radiating element of claim 9, wherein the conductive patch
includes a first portion that is implemented on a first metal layer
of a printed circuit board and a second portion that is implemented
on the second metal layer of the printed circuit board.
11. The radiating element of claim 1, wherein the printed circuit
board further includes a conductive ring that at least partially
surrounds a periphery of the conductive patch and that encloses
each of the first through fourth slots.
12. A method of suppressing a common mode resonance in a base
station antenna having a reflector, an array of first radiating
elements that are configured to operate in a first operating
frequency band and an array of second radiating elements that are
configured to operate in a second operating frequency band, where
each second radiating element includes a radiator unit that is
positioned forwardly of the reflector and at least one coaxial feed
cable that connects to the radiator unit, the method comprising:
electrically connecting an outer conductor of a first of the
coaxial feed cables that feeds a first of the second radiating
elements to the reflector at a grounding position that is selected
so that the physical distance of the radio frequency ("RF")
transmission path that extends between the grounding position and
the radiator unit of the first of the second radiating elements is
a distance that is not resonant at any frequency in the first
operating frequency band.
13. The method of claim 12, wherein the grounding position is a
position where an outer conductor of the first of the coaxial feed
cables is galvanically connected to a rear surface of the
reflector.
14. The method of claim 13, where the first of the coaxial feed
cables is galvanically connected to a rear surface of the reflector
by exposing a portion of the outer conductor and soldering the
exposed portion of the outer conductor to the reflector.
15. The method of claim 12, wherein the first of the coaxial feed
cables extends between the radiator unit and a printed circuit
board, and wherein the printed circuit board includes a grounding
tab where a ground conductor of the printed circuit board is
coupled to the reflector.
16. The method of claim 15, wherein the physical distance of the RF
transmission path that extends between the grounding position and
the radiator unit of the first of the second radiating elements is
the sum of the length of the first of the coaxial feed cables and a
distance between the location where the first of the coaxial feed
cables connects to the printed circuit board and the grounding
tab.
17. The method of claim 12, wherein the physical distance of the RF
transmission path that extends between the grounding position and
the radiator unit of the first of the second radiating elements is
not a multiple of a quarter wavelength of any frequency in the
first operating frequency band.
18. The method of claim 12, wherein a second of the coaxial feed
cable also feeds the first of the second radiating elements, and
wherein a conductive stub physically and electrically connects an
outer conductor of the first of the coaxial feed cables to an outer
conductor of the second of the coaxial feed cables.
19. The method of claim 18, wherein the radiator unit of first of
the second radiating elements is mounted forwardly from the
reflector at a distance that is greater than one-quarter of a
wavelength corresponding to the center frequency of the second
operating frequency band, and the conductive stub is located at
approximately one quarter of the wavelength corresponding to the
center frequency of the second operating frequency band of the
radiating element from the radiator unit.
20. The method of claim 19, wherein the conductive stub is located
closer to the reflector than it is to the radiator unit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority to Chinese Patent
Application 202010061865.4, filed Jan. 20, 2020, and to Chinese
Patent Application 202010168550.X, filed Mar. 12, 2020, the entire
content of both of which are incorporated herein by reference.
BACKGROUND
The present invention generally relates to radio communications
and, more particularly, to radiating elements for base station
antennas used in cellular communications systems.
Cellular communications systems are well known in the art. In a
cellular communications system, a geographic area is divided into a
series of regions that are referred to as "cells" which are served
by respective base stations. The base station may include one or
more base station antennas that are configured to provide two-way
radio frequency ("RF") communications with mobile subscribers that
are within the cell served by the base station. The base station
antennas are often mounted on a tower, with the radiation patterns
(also referred to herein as "antenna beams") that are generated by
the base station antennas directed outwardly. Many cells are
divided into "sectors." In perhaps the most common configuration, a
hexagonally-shaped cell is divided into three 120.degree. sectors,
and each sector is served by one or more base station antennas that
generate antenna beams that have an azimuth Half Power Beamwidth
(HPBW) of approximately 65.degree.. Typically, a base station
antenna includes multiple phase-controlled antenna arrays that each
include a plurality radiating elements that are arranged in one or
more vertical columns when the antenna is mounted for use. Herein,
"vertical" refers to a direction that is perpendicular to the
horizontal plane that is defined by the horizon. Each antenna array
generates a respective antenna beam, or two antenna beams if the
antenna array is formed with dual-polarized radiating elements. The
phase controlled antenna arrays include columns of radiating
elements (as opposed to a single radiating element) in order to
narrow the vertical or "elevation" beamwidth of the antenna beam,
which may both increase the gain of the array and reduce
interference with adjacent cells.
In order to accommodate the ever-increasing volume of cellular
communications, cellular operators have added cellular service in a
variety of new frequency bands. Cellular operators have applied a
variety of approaches to support service in these new frequency
bands, including increasing the number of linear arrays (or planar
arrays) of radiating elements per antenna. As more columns of
radiating elements are added to a typical antenna, efforts have
been made to decrease the sizes of the radiating elements in order
to reduce interactions between adjacent columns of radiating
elements. Additionally, as the number of radiating elements
included in an antenna increases, the advantage of lowering the
unit cost of the radiating elements increases.
SUMMARY
Pursuant to embodiments of the present invention, radiating
elements are provided that include a conductive patch having first
and second slots that each extend along a first axis and third and
fourth slots that each extend along a second axis that is
perpendicular to the first axis, a feed network that includes first
through fourth feed lines, each feed line crossing a respective one
of the first through fourth slots, and a conductive ring that at
least partially surrounds a periphery of the conductive patch and
that encloses each of the first through fourth slots.
In some embodiments, the conductive ring may be a continuous ring
that completely surrounds the conductive patch when the radiating
element is viewed in plan view.
In some embodiments, the conductive ring may have a plurality of
sections, and each section may enclose a respective one of the
first through fourth slots.
In some embodiments, the feed network may further include a first
input, a first power divider that is coupled to the first input, a
second input, and a second power divider that is coupled to the
second input, and the first and second feed lines may be coupled to
respective first and second outputs of the first power divider, and
the third and fourth feed lines may be coupled to respective first
and second outputs of the second power divider.
In some embodiments, at least a portion of the conductive patch may
be implemented on a first metal layer of a printed circuit board,
where the first through fourth feed lines comprise metal traces on
a second metal layer of the printed circuit board, and where each
of the first through fourth slots extend to the periphery of the
conductive patch.
In some embodiments, the second metal layer of the printed circuit
board may further include a plurality of metal pads that are each
electrically connected to the conductive patch via one or more
plated through holes that extend between the first and second metal
layers of the printed circuit board.
In some embodiments, the conductive patch may include a first
portion that is implemented on a first metal layer of a printed
circuit board and a second portion that is implemented on a
different metal layer of the printed circuit board. In some
embodiments, the different metal layer of the printed circuit board
may be the second metal layer of the printed circuit board.
In some embodiments, the conductive ring may be electrically
floating. In other embodiments, the conductive ring may be
electrically connected to the conductive patch. In some
embodiments, the conductive ring may be coplanar with at least a
portion of the conductive patch.
Pursuant to further embodiments of the present invention, radiating
elements for a base station antenna are provided that include a
printed circuit board that includes a conductive patch having first
and second slots that each extend along a first axis and third and
fourth slots that each extend along a second axis that is
perpendicular to the first axis, a first coaxial cable and a second
coaxial cable that each extend from a reflector of the base station
antenna to the printed circuit board, and a conductive stub that
physically and electrically connects an outer conductor of the
first coaxial cable to an outer conductor of the second coaxial
cable.
In some embodiments, the printed circuit board may be mounted
forwardly from the reflector at a distance that is greater than
one-quarter of a wavelength corresponding to the center frequency
of the operating frequency band of the radiating element.
In some embodiments, the conductive stub may be located at
approximately one quarter of the wavelength corresponding to the
center frequency of the operating frequency band of the radiating
element from the printed circuit board. In some embodiments, the
conductive stub may be located closer to the reflector than it is
to the printed circuit board.
In some embodiments, the outer conductors of the first and second
coaxial cables may be soldered to the printed circuit board.
In some embodiments, the radiating element may further include
first and second conductive tubes that are positioned adjacent the
first and second coaxial cables.
In some embodiments, the printed circuit board may further include
a feed network that has a first input that is electrically
connected to an inner conductor of the first coaxial cable, a first
power divider that is coupled to the first input, first and second
transmission lines that extend from the first power divider to
cross the respective first and second slots, a second input that is
electrically connected to an inner conductor of the second coaxial
cable, a second power divider that is coupled to the second input,
and third and fourth transmission lines that extend from the second
power divider to cross the respective third and fourth slots.
In some embodiments, the conductive patch may be implemented at
least partially on a first metal layer of the printed circuit
board, where the feed network is implemented on a second metal
layer of the printed circuit board, where the second metal layer
further includes a plurality of metal pads that are each
electrically connected to the conductive patch, and where each of
the first through fourth slots extend to a periphery of the
conductive patch.
Pursuant to still further embodiments of the present invention,
radiating elements for a base station antenna are provided that
include a printed circuit board that includes a conductive patch
having first and second slots that each extend along a first axis
and third and fourth slots that each extend along a second axis
that is perpendicular to the first axis and a feed stalk that
mounts the printed circuit board in front of a reflector of the
base station antenna. A first metal layer of the printed circuit
board includes a first portion of the conductive patch and a second
metal layer of the printed circuit board includes a second portion
of the conductive patch.
In some embodiments, the first portion of the conductive patch may
be capacitively coupled to the second portion of the conductive
patch. In other embodiments, the first portion of the conductive
patch may be galvanically connected to the second portion of the
conductive patch.
In some embodiments, the printed circuit board may further include
a feed network that includes a first input, a first power divider
that is coupled to the first input, and first and second
transmission lines that extend from the first power divider to
cross the respective first and second slots, and a second input, a
second power divider that is coupled to the second input, and third
and fourth transmission lines that extend from the second power
divider to cross the respective third and fourth slots.
In some embodiments, the feed network may be implemented on the
second metal layer of the printed circuit board.
In some embodiments, the first portion of the conductive patch may
comprise a central portion of the conductive patch and the second
portion of the conductive patch may comprise a first annular-shaped
metal layer having an inner portion that overlaps the central
portion of the conductive patch and an exterior portion that
extends outwardly beyond the central portion of the conductive
patch.
In some embodiments, the conductive patch may further include a
third portion that comprises a second annular-shaped metal layer
having an inner portion that overlaps the first annular-shaped
metal layer of the second portion of the conductive patch and an
exterior portion that extends outwardly beyond the first
annular-shaped metal layer of the second portion of the conductive
patch.
In some embodiments, the third portion of the conductive patch may
be implemented in the first metal layer.
In some embodiments, each of the first through fourth slots may
extend to a periphery of the conductive patch.
Pursuant to additional embodiments of the present invention,
radiating elements for a base station antenna are provided that
include a conductive patch having first through fourth slots that
each extend along a first axis and fifth through eighth slots that
each extend along a second axis that is perpendicular to the first
axis, each of the first through fourth slots extending to a
periphery of the conductive patch, the first through eighth slots
dividing the conductive patch into four conductive arms and a first
trace that extends from the first conductive arm to the second
conductive arm to separate the first slot from the second slot.
In some embodiments, a second trace that extends from the second
conductive arm to the third conductive arm to separate the fifth
slot from the sixth slot, a third trace that extends from the third
conductive arm to the fourth conductive arm to separate the third
slot from the fourth slot, and a fourth trace that extends from the
fourth conductive arm to the first conductive arm to separate the
seventh slot from the eighth slot.
In some embodiments, the radiating element may further include a
feed stalk that mounts a printed circuit board in front of a
reflector of the base station antenna.
Pursuant to further embodiments of the present invention, methods
of suppressing a common mode resonance in a base station antenna
are provided. The base station antenna may include at least a
reflector, an array of first radiating elements that are configured
to operate in a first operating frequency band and an array of
second radiating elements that are configured to operate in a
second operating frequency band. Each second radiating element
includes a radiator unit that is positioned forwardly of the
reflector and at least one coaxial feed cable that connects to the
radiator unit. Pursuant to these methods, an outer conductor of a
first of the coaxial feed cables that feeds a first of the second
radiating elements is electrically connected to the reflector at a
grounding position that is selected so that the physical distance
of the RF transmission path that extends between the grounding
position and the radiator unit of the first of the second radiating
elements is a distance that is not resonant at any frequency in the
first operating frequency band.
In some embodiments, the grounding position may be a position where
an outer conductor of the first of the coaxial feed cables is
galvanically connected to a rear surface of the reflector. For
example, the first of the coaxial feed cables may be galvanically
connected to a rear surface of the reflector by exposing a portion
of the outer conductor and soldering the exposed portion of the
outer conductor to the reflector. The first of the coaxial feed
cables may extend between the radiator unit and a printed circuit
board, and the printed circuit board may include a grounding tab
where a ground conductor of the printed circuit board is coupled to
the reflector.
In some embodiments, the physical distance of the RF transmission
path that extends between the grounding position and the radiator
unit of the first of the second radiating elements may be the sum
of the length of the first of the coaxial feed cables and a
distance between the location where the first of the coaxially feed
cables connects to the printed circuit board and the grounding
tab.
The physical distance of the RF transmission path that extends
between the grounding position and the radiator unit of the first
of the second radiating elements may, for example, not be a
multiple of a quarter wavelength of any frequency in the first
operating frequency band.
In some embodiments, a second of the coaxial feed cable may also
feed the first of the second radiating elements, and a conductive
stub may physically and electrically connect an outer conductor of
the first of the coaxial feed cables to an outer conductor of the
second of the coaxial feed cables. In such embodiments, the
radiator unit of first of the second radiating elements may be
mounted forwardly from the reflector at a distance that is greater
than one-quarter of a wavelength corresponding to the center
frequency of the second operating frequency band, and the
conductive stub may be located at approximately one quarter of the
wavelength corresponding to the center frequency of the second
operating frequency band of the radiating element from the radiator
unit. In some embodiments, the conductive stub may be located
closer to the reflector than it is to the radiator unit.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a side perspective view of a base station antenna
according to embodiments of the present invention.
FIG. 1B is a schematic front view of the base station antenna of
FIG. 1A with the radome removed.
FIGS. 2A and 2B are a side perspective view and an exploded side
perspective view, respectively, of a dual-polarized radiating
element according to embodiments of the present invention.
FIG. 3A is a front view of a radiator unit of the dual-polarized
radiating element of FIGS. 2A-2B.
FIGS. 3B and 3C are graphs of the cross-polarization discrimination
performance of the radiating element of FIG. 3A when implemented
both without and with a conductive ring.
FIGS. 4A and 4B are front views of radiator units according to
further embodiments of the present invention that may be used in
place of the radiator unit of FIG. 3A.
FIG. 5A is a perspective rear view of a radiating element according
to further embodiments of the present invention in which the outer
conductors of the feed coaxial cables are soldered together.
FIGS. 5B and 5C are simulated azimuth patterns for the radiating
element of FIG. 5A without and with the conductive stubs,
respectively.
FIGS. 5D and 5E are graphs showing the simulated return loss for
the radiating element of FIG. 5A without and with the conductive
stubs, respectively.
FIGS. 5F and 5G are graphs showing the simulated port-to-port
isolation for the radiating element of FIG. 5A without and with the
conductive stubs, respectively.
FIG. 6 is a perspective rear view of a radiating element according
to still further embodiments of the present invention that includes
a pair of metal rods that are soldered to the feed cables.
FIG. 7 is a front view of a radiator unit according to further
embodiments of the present invention.
FIG. 8 is a front view of a radiator unit according to still
further embodiments of the present invention.
FIGS. 9A and 9B are a front view and a back view, respectively, of
a radiator unit printed circuit board according to further
embodiments of the present invention with the feed network of the
radiator unit omitted.
FIGS. 10A and 10B are a front view and a back view, respectively,
of a radiator unit printed circuit board according to still further
embodiments of the present invention with the feed network
omitted.
FIGS. 11A and 11B are a front view and a back view, respectively,
of a radiator unit printed circuit board according to yet
additional embodiments of the present invention with the feed
network of the radiator unit omitted.
FIGS. 12A and 12B are a front view and a back view, respectively,
of a radiator unit printed circuit board according to yet
additional embodiments of the present invention.
FIGS. 13A and 13B are shadow front and back views, respectively, of
the radiator unit printed circuit board of FIGS. 12A and 12B.
FIG. 14A is a side view of a portion of a base station antenna that
includes a pair of radiating elements mounted on a reflector that
are fed by a power divider printed circuit board that is mounted
behind the reflector.
FIG. 14B is a rear view of the power divider printed circuit board
of FIG. 14A.
FIG. 15A is a side view of a sheet metal based radiating element
according to still further embodiments of the present
invention.
FIG. 15B is a schematic view of a lower portion of one of the metal
plates of the feed stalk of the radiating element of FIG. 15A
illustrating how a feed line may be mounted thereon to form a
microstrip feed line.
FIG. 15C is a front perspective shadow view of a radiator unit of
the radiating element of FIG. 15A.
FIG. 15D is a front shadow view of the radiator unit of FIG.
15C.
FIG. 15E is a front shadow view of a modified version of the
radiator unit of FIGS. 15C-15D.
FIGS. 15F and 15G are a front perspective shadow view and a front
shadow view, respectively, of another modified version of the of
the radiator unit of FIGS. 15C-15D.
DETAILED DESCRIPTION
Pursuant to embodiments of the present invention, small, low-cost
dual-polarization radiating elements are provided that are suitable
for use in base station antennas. In some embodiments, the
radiating elements may be configured to operate in the 1427-2690
MHz frequency band or a portion thereof. For example, in some
embodiments the radiating elements may be designed to operate in
the 1695-2690 MHz frequency band. It will be appreciated, however,
that the radiating elements according to embodiments of the present
invention may be scaled to operate in other frequency bands. The
radiating elements may exhibit high levels of port-to-port
isolation, good cross-polarization discrimination, low insertion
loss and suitable azimuth beamwidth performance across a wide
operating frequency band.
In some embodiments, the radiating elements may include a radiator
unit and a feed stalk. The feed stalk may be used to mount the
radiator unit a suitable distance forwardly of a reflector of a
base station antenna. The radiating element may optionally include
a director and a director support. The radiator unit may comprise a
conductive patch that has first and second slots that extend along
a first axis and third and fourth slots that extend along a second
axis that is perpendicular to the first axis. Each of the first
through fourth slots may extend from a periphery of the conductive
patch towards the middle or "central region" of the conductive
patch, and the four slots may divide the conductive patch into four
arms. Each arm may be a generally pie-shaped wedge in some
embodiments, and the four arms may be electrically connected to
each other in a central region of the conductive patch.
In some embodiments, the radiator unit may be implemented using a
printed circuit board. In such embodiments, the printed circuit
board may include a first metallization layer that includes at
least a portion of a conductive patch and a second metallization
layer that includes a feed network, where the two metal layers are
separated by a dielectric layer. In some embodiments, the
conductive patch may be implemented in its entirety on the first
metallization layer of the printed circuit board, while in other
embodiments, a second portion of the conductive patch may be
implemented on a different metallization layer which may be the
second metallization layer and/or a third metallization layer in
various embodiments. In other embodiments, the conductive patch may
be a sheet metal patch and any suitable feed network may be used to
feed RF signals to the slots in the sheet metal patch. The
conductive patch may have any appropriate shape including a
circular shape, a square shape, an octagonal shape, etc. As shown
in the drawings, the conductive patch may also be a variation
and/or an approximation of such shapes.
The feed network may include first through fourth feed lines, where
each feed line crosses a respective one of the first through fourth
slots. The feed lines may be implemented as microstrip transmission
lines or coplanar waveguide transmission lines in example,
non-limiting embodiments. The feed network may also include a first
input, a first power divider that is coupled to the first input, a
second input, and a second power divider that is coupled to the
second input. The first and second feed lines may be coupled to
respective first and second outputs of the first power divider, and
the third and fourth feed lines may be coupled to respective first
and second outputs of the second power divider.
In some embodiments, the radiator unit may further include a
conductive ring that at least partially surrounds the periphery of
the conductive patch and encloses each of the first through fourth
slots. In some embodiments, the conductive ring may be a continuous
metal ring that completely surrounds the conductive patch, while in
other embodiments, the conductive ring may comprise a plurality of
sections, wherein each section encloses a respective one of the
first through fourth slots. The conductive ring may be electrically
connected to ground or may be electrically floating. The conductive
ring may capacitively load the conductive patch, which may improve
the cross-polarization discrimination performance of the radiating
element, particularly at lower frequencies.
In some embodiments, the feed stalk may comprise a pair of coaxial
feed cables that couple respective first and second RF ports of an
antenna to the radiator unit. The feed stalk may further include a
structural support such as, for example, a plastic support stalk.
The structural support may be used to mount the radiator unit in
front of the reflector and/or to maintain the coaxial feed cables
in proper position for connecting to the radiator units. In order
to increase the bandwidth of the radiating element, the feed stalk
may mount the radiator unit more than a quarter wavelength in front
of the reflector of the base station antenna in which the radiating
element is used, where the wavelength refers to the wavelength
corresponding to the center frequency of the operating frequency
band of the radiating element. In some embodiments, the outer
conductors of the two coaxial feed cables may be soldered or
otherwise electrically connected together. For example, the two
outer conductors may be soldered together at a distance of
approximately one quarter wavelength from the radiator unit. This
may improve the port-to-port isolation performance of the radiating
element. A pair of metal rods may be provided on either side of the
coaxial feed cables. The rods may provide a more symmetric
structure behind the radiator unit, which may help improve the
port-to-port isolation performance of the radiating element.
In still other embodiments, the conductive patch may be elongated
in the vertical direction, which may narrow the elevation beamwidth
and/or reduce the magnitude of the grating lobes in the antenna
beam formed by the radiating element. In still other embodiments,
the slots in the conductive patch may extend from a center of the
conductive patch outwardly, and may be closed off at the periphery
of the metal patch. In yet other embodiments, four meandered traces
may be used to electrically connect adjacent arms of the conductive
patch near the periphery of the conductive patch.
Pursuant to still further embodiments of the present invention,
techniques are provided for suppressing common mode resonances that
the coaxial feed cables used to feed RF signals to the
above-described radiator units may generate in the responses of
other nearby radiating elements that operate in different operating
frequency bands. Pursuant to these techniques, the outer conductor
of each coaxial feed cable may be electrically connected to a
common ground reference such as the reflector of the base station
antenna at a location where the length of the RF transmission path
that extends between the grounding location and the radiator unit
may not be a length that is resonant in the operating frequency
band of other nearby radiating elements that operate in different
frequency bands. The length of each RF transmission path may be the
length of the coaxial feed cable plus the length of any additional
path between the end of the coaxial feed cable and the grounding
location. Ideally, the length of the RF transmission path that
extends between the grounding location and the radiator unit may be
kept as short as possible in order to reduce insertion losses, but
is also selected so that the electrical length of the monopole
formed by the coaxial feed cable (and other RF transmission path to
the grounding location) is not resonate in the operating frequency
band of the other nearby radiating elements.
Pursuant to still further embodiments of the present invention,
radiating elements are provided that include a conductive patch
having first and second slots that each extend along a first axis
and third and fourth slots that each extend along a second axis
that is perpendicular to the first axis. These radiating elements
also include a feed network that includes first through fourth feed
lines, each feed line crossing a respective one of the first
through fourth slots. The first and second feed lines are forward
of a first major surface of the conductive patch and the third and
fourth feed lines are rearward of a second major surface of the
conductive patch.
In some embodiment, the conductive patch may be formed of sheet
metal. The radiating element may also include a metal stalk that
includes first and second air microstrip transmission lines. A
signal trace of the first air microstrip transmission line and the
first and second feed lines may be formed as a first monolithic
feed structure, and a signal trace of the second air microstrip
transmission line and the third and fourth feed lines may be formed
as a second monolithic feed structure. The first monolithic feed
structure may extend through an opening in the conductive patch,
while the second monolithic feed structure does not extend through
any opening in the conductive patch. In some embodiments, outer
edges of the conductive patch are bent (e.g., upwardly and/or
downwardly) at an angle of at least 30.degree. with respect to an
inner portion of the conductive patch.
The radiating elements according to embodiments of the present
invention may have a number of advantages. First, the radiating
elements may have small physical footprints, and hence may exhibit
improved column-to-column isolation. Second, the radiating elements
may be inexpensive to manufacture, and may require fewer soldered
connections than many conventional radiating elements. The reduced
number of solder joints may simplify assembly while also reducing
the number of potential sources for passive intermodulation
distortion. Additionally, the radiating elements may have very
large operating frequency bands while meeting all necessary
performance metrics.
Embodiments of the present invention will now be discussed in
greater detail with reference to the accompanying figures.
FIGS. 1A and 1B illustrate a base station antenna 10 according to
certain embodiments of the present invention. In particular, FIG.
1A is a front perspective view of the base station antenna 10, and
FIG. 1B is a front view of the antenna 10 with the radome thereof
removed to illustrate the inner components of the antenna. Any of
the radiating elements according to embodiments of the present
invention that are described herein may be used to implement the
radiating elements (described below) in base station antenna
10.
As shown in FIG. 1A, the base station antenna 10 is an elongated
structure that extends along a longitudinal axis L. The base
station antenna 10 may have a tubular shape with a generally
rectangular cross-section. The antenna 10 includes a radome 12 and
a top end cap 14, which may or may not be integral with the radome
12. The antenna 10 also includes a bottom end cap 16 which includes
a plurality of connectors 18 mounted therein. The antenna 10 is
typically mounted in a vertical configuration (i.e., the
longitudinal axis L may be generally perpendicular to a plane
defined by the horizon when the antenna 10 is mounted for normal
operation).
As shown in FIG. 1B, the base station antenna 10 includes an
antenna assembly 20 that may be slidably inserted into the radome
12. The antenna assembly 20 includes a ground plane structure 22
that has a reflector 24. Various mechanical and electronic
components of the antenna 10 may be mounted behind the reflector 24
such as, for example, phase shifters, remote electronic tilt
("RET") units, mechanical linkages, a controller, diplexers, and
the like. The reflector 24 may comprise or include a metallic
surface that serves as both a reflector and as a ground plane for
the radiating elements of the antenna 10.
A plurality of dual-polarized low-band radiating elements 32 and a
plurality of dual-polarized high-band radiating elements 42 are
mounted to extend forwardly from the reflector 24. The low-band
radiating elements 32 are mounted in a vertical column to form a
linear array 30 of low-band radiating elements 32, and the
high-band radiating elements 42 are mounted in two vertical columns
to form two linear arrays 40-1, 40-2 of high-band radiating
elements 42. The linear array 30 of low-band radiating elements 32
may be positioned between the two linear arrays 40-1, 40-2 of
high-band radiating elements 42. Each linear array 30, 40-1, 40-2
may be used to form a pair of antenna beams, namely a first antenna
beam having a+45.degree. polarization and a second antenna beam
having a-45.degree. polarization. Note that herein when multiple
like elements are provided, the elements may be identified by
two-part reference numerals. The full reference numeral (e.g.,
linear array 40-2) may be used to refer to an individual element,
while the first portion of the reference numeral (e.g., the linear
arrays 40) may be used to refer to the elements collectively.
The low-band radiating elements 32 may be configured to transmit
and receive signals in a first frequency band. In some embodiments,
the first frequency band may comprise the 694-960 MHz frequency
range or a portion thereof. The high-band radiating elements 42 may
be configured to transmit and receive signals in a second frequency
band. In some embodiments, the second frequency band may comprise
the 1427-2690 MHz frequency range or a portion thereof. It will be
appreciated that the number of linear arrays of radiating elements
may be varied from what is shown in FIG. 1B, as may the number of
radiating elements per linear array and/or the positions of the
linear arrays. It will also be appreciated that multi-column arrays
may be used instead of and/or in addition to the linear arrays of
radiating elements.
As noted above, embodiments of the present invention provide low
cost, high performance dual-polarized radiating elements that may
be used, for example, to implement each of the high-band radiating
elements 42 shown in FIG. 1B. A first embodiment of such a
dual-polarized radiating element 100 will now be described with
reference to FIGS. 2A-3C. The radiating element 100 may be used,
for example, as each of the high-band radiating elements 42 in base
station antenna 10 of FIGS. 1A-1B.
FIGS. 2A and 2B are a side perspective view and an exploded side
perspective view, respectively, of a dual-polarized radiating
element 100 according to embodiments of the present invention. As
shown in FIGS. 2A-2B, the radiating element 100 includes a feed
stalk 110, a radiator unit 140, and a director unit 190.
The feed stalk 110 may be used to mount the radiating element 100
to extend forwardly from the reflector 24 of base station antenna
10. The feed stalk 110 in the illustrated embodiment includes a
support stalk 120 which may be made, for example, of plastic, and a
pair of coaxial feed cables 130-1, 130-2. The radiator unit 140 may
be mounted on the plastic support stalk 120 in some embodiments.
The plastic support stalk 120 may include internal guide features
122 that are used to maintain the coaxial feed cables 130-1, 130-2
in their proper positions, as well as a mounting base 124 that is
used to mount the plastic support stalk 120 in openings in the
reflector 24 (FIG. 1B) so that the plastic support stalk 120
extends forwardly from the reflector 24. The coaxial feed cables
130-1, 130-2 may be routed from other components of the base
station antenna 10 (e.g., from electromechanical phase shifter
assemblies) that are mounted rearwardly of the reflector 24 to the
opening in the reflector 24 in which the plastic support stalk 120
is mounted. The coaxial feed cables 130-1, 130-2 may extend through
the opening and may be routed by the guide features 122 in the
support stalk 120 to the radiator unit 140. The coaxial feed cables
130-1, 130-2 may be physically and/or electrically connected to the
radiator unit 140. In particular, the outer conductors of the
coaxial feed cables 130 may be electrically connected to a
conductive patch (see FIG. 3A) of the radiator unit 140, while the
center conductors of coaxial feed cables 130 may be coupled to a
feed network (see FIG. 3A) of the radiator unit 140.
In order to increase the bandwidth of radiating element 100, the
feed stalk 110 may be designed to mount the radiator unit 140 more
than a quarter wavelength in front of the reflector 24 of base
station antenna 100, where the wavelength refers to the wavelength
corresponding to the center frequency of the operating frequency
band of the radiating element 100.
While the support stalk 110 of FIGS. 2A-2B includes a plastic
support 120 and a pair of coaxial feed cables 130-1, 130-2, it will
be appreciated that the plastic support 120 may be omitted in other
embodiments, and that the coaxial feed cables 130-1, 130-2 can be
replaced with other feed structures (e.g., printed circuit board
feeds, metal transmission line feeds, etc.) in still other
embodiments.
The director unit 190 may comprise a director support 192 and a
director 194. The director 194 may comprise, for example, a flat
piece of metal that is somewhat smaller than a conductive patch
that is included in the radiator unit 140. The director support 192
is used to mount the director 194 at a suitable height above the
radiator unit 140. The director 194 may help narrow the radiation
pattern of the radiating element 100 in both the azimuth and
elevation planes.
The radiator unit 140 included in radiating element 100 will now be
described with reference to FIGS. 3A-3C. It will be appreciated,
however, that a wide variety of different radiator unit designs may
be used. Examples of other radiator units that may be used in place
of radiator unit 140 will be discussed below with reference to
FIGS. 4A-4B and 6-11B.
FIG. 3A is a front view of the radiator unit 140 of the
dual-polarized radiating element 100 of FIGS. 2A-2B. The radiator
unit 140 may be implemented using a printed circuit board 142 that
has a first metallization layer 144 and a second metallization
layer 146 that are separated by a dielectric layer 148. To simplify
the drawing, the dielectric layer 148 is not shown in FIG. 3A
(although suitable dielectric layers that could be used to
implement dielectric layer 148 are shown, for example, in FIGS.
9A-10B), and the first and second metallization layers 144, 146 are
depicted using different colors. In some embodiments, the first
metallization layer 144 may be a rear metallization layer and the
second metallization layer 146 may be a front metallization layer
when the radiator unit 140 is implemented in a radiating element
that is mounted in a base station antenna.
As shown in FIG. 3A, a conductive patch 150 may be formed in the
first metallization layer 144. The conductive patch 150 may
comprise a copper pattern that is formed on the rear of the
dielectric layer 148 of the printed circuit board 142. Four slots
152-1 through 152-4 are formed in the conductive patch 150 where
the metallization is omitted to expose the dielectric layer 148.
Each slot 152 may extend radially from a respective point near the
center of the conductive patch 150 to the periphery of the
conductive patch 150. The slots 152 may divide the conductive patch
150 into four arms 154-1 through 154-4. Each slot 152 may be
rotationally offset from adjacent slots by -90.degree. and
90.degree., respectively. Thus, the first and second slots 152-1,
152-2 may extend along a first axis L1 and the third and fourth
slots 152-3, 152-4 may extend along a second axis L2 that is
perpendicular to the first axis L1. The first slot 152-1 may extend
at an angle of -45.degree., the second slot 152-2 may extend at an
angle of +135.degree., the third slot 152-3 may extend at an angle
of +45.degree., and the fourth slot 152-4 may extend at an angle of
-135.degree.. Each of the first through fourth slots 152-1 through
152-4 may extend from a periphery of the conductive patch 150
towards the middle or "central region" of the conductive patch 150,
and the four slots 152 may divide the conductive patch 150 into the
four arms 154-1 through 154-4. Each arm 154 may be a generally
pie-shaped wedge, and the four arms 154 may be electrically
connected to each other in a central region of the conductive patch
150.
As shown in FIG. 3A, the width of each slot 152 may be expanded at
one or both ends thereof to provide enlarged slot ends 156 in some
embodiments. Additionally, some of the metallization (along with
the underlying dielectric material of the printed circuit board
142) may be removed/omitted in, for example, central regions of
some of the patch arms 154 to create openings 158. Legs of the
director support 192 may be mounted in these openings 158.
The second metallization layer 146 of printed circuit board 142 may
face forwardly, and may include a feed network 160 that is used to
couple RF signals to and from the conductive patch 150. The feed
network 160 may include first through fourth feed lines 166-1
through 166-4, where each feed line 166-1 through 166-4 crosses a
respective one of the first through fourth slots 152-1 through
152-4. The feed lines 166 may be implemented as microstrip
transmission lines in some embodiments. As shown in FIG. 3A, in
other embodiments, metal pads 167 may be provided on one or both
sides of some or all of the feed lines 166, and these metal pads
167 may be electrically connected to the underlying conductive
patch 150 via plated through holes (not shown) that extend through
the dielectric layer 148 of the printed circuit board 142. As the
conductive patch 150 is connected to ground potential, the metal
pads 167 may convert the feed lines 166 from microstrip
transmission lines into coplanar waveguide transmission lines. It
will also be appreciated that any other suitable type of feed line
may be used including, for example, cables or strip lines or
combinations of any of the above.
The feed network 160 may further include first and second inputs
162-1, 162-2 and first and second power dividers 164-1, 164-2. The
inputs 162 may each comprise a metal pad. A hole 163 may extend
through a center of each metal pad 162 and through the dielectric
layer 148 of the printed circuit board 142 so that center
conductors of the respective coaxial feed cables 130-1, 130-2 may
be inserted through the printed circuit board 142 and through the
respective metal pads 162-1, 162-2. The center conductors of
coaxial feed cables 130-1, 130-2 may be soldered (or otherwise
electrically connected) to the respective metal pads 162-1, 162-2.
The outer conductors of coaxial feed cables 130-1, 130-2 may be
soldered (or otherwise electrically connected) to the conductive
patch 150. Each input pad 162-1, 162-2 may act as a respective
power divider 164-1, 164-2 that splits an RF signal that is input
to the respective input pads 162. Feed lines 166-1 and 166-2 extend
from the two outputs of the first power divider 164-1 and cross the
respective first and second slots 152-1, 152-2, and feed lines
166-3 and 166-4 extend from the two outputs of the second power
divider 164-2 and cross the respective third and fourth slots
152-3, 152-4. In the depicted embodiment, each feed line 166-1
through 166-4 terminates into a respective one of four quarter
wavelength stubs 168-1 through 168-4. As a result, RF signals that
are input on feed lines 166-1 through 166-4 feed the respective
slots 152-1 through 152-4. In particular, when feed lines 166-1 and
166-2 are excited, slots 152-1 and 152-2 are fed, causing the
conductive patch 150 to radiate RF energy having a-45.degree.
polarization. Likewise, when feed lines 166-3 and 166-4 are
excited, slots 152-3 and 152-3 are fed, causing the conductive
patch 150 to radiate RF energy having a+45.degree.
polarization.
As is further shown in FIG. 3A, the radiator unit 140 may further
include a conductive ring 170 that at least partially surrounds the
periphery of the conductive patch 150 and that encloses each of the
first through fourth slots 152-1 through 152-4. In the depicted
embodiment, the conductive ring 170 is a thin, continuous metal
ring that is implemented on the rear metallization layer 144 that
completely surrounds the conductive patch 150. The conductive ring
170 may capacitively load the conductive patch 150. It has been
found that this may improve the cross polarization discrimination
performance of the radiating element 100. FIGS. 3B and 3C are
graphs of the cross-polarization discrimination performance of
radiating element 100 both with and without the conductive ring
170. As shown, without the ring (FIG. 3B), the cross-polarization
discrimination is as low as 6.4 dB, whereas with the ring the
cross-polarization discrimination is greater than 7.75 dB across
the entire 1.695-2.690 GHz operating frequency band of the
radiating element 100.
FIGS. 4A and 4B are front views of radiator units 140A, 140B,
respectively, according to further embodiments of the present
invention that may be used in place of the radiator unit 140 of
FIG. 3A. FIGS. 4A and 4B only illustrate the conductive patch 150
and the conductive rings 170A, 170B and do not illustrate the feed
network to simplify the drawings. It will be appreciated that the
feed network 160 of FIG. 3A may be used as the feed networks for
radiator unit 140A of FIG. 4A or for radiator unit 140B of FIG. 4B.
The slots 152A, 152B in conductive patches 150A, 150B have slightly
different designs from the slots 152 in conductive patch 150, and
the mounting holes 158 are omitted in conductive patches 150A,
150B, but otherwise the conductive patches 150, 150A and 150B are
identical.
As shown in FIG. 4A, the conductive ring 170A of radiator unit 140A
is identical to conductive ring 170, except that four tabs 172 are
provided that electrically short the conductive ring 170A to the
conductive patch 150A. As a result, the conductive ring 170A is
maintained at ground potential and is not electrically floating as
is the conductive ring 170 of FIG. 3A. As shown in FIG. 4B, the
conductive ring 170B is similar to the conductive ring 170A, but is
a discontinuous ring that includes four segments 174 that are
separated by gaps 176. Each segment 174 is electrically connected
to the conductive patch 150B by a pair of tabs 172.
FIG. 5A is a perspective rear view of a radiating element 200
according to further embodiments of the present invention in which
the outer conductors of the feed coaxial cables are electrically
connected to each other by a conductive stub.
The radiating element 200 may be identical to the radiating element
100 discussed above with one exception, which is that the outer
conductors of coaxial feed cables 130-1, 130-2 are electrically
connected together by a conductive stub 232 in radiating element
200. Note that various features of radiating element 200 are not
shown in FIG. 5A, such as the stalk support 120 of the director
unit 190.
The outer conductors of each coaxial feeder cable 130-1, 130-2 are
nominally at ground potential. However, the coaxial feed cables
130-1, 130-2 may not connect to a common ground in the vicinity of
radiating element 200 and, as a result, the two outer conductors
may not actually be at a common potential. This difference in
potential may result in unbalanced currents flowing on the coaxial
feed cables 130-1, 130-2, which may degrade both the port-to-port
isolation and the cross-polarization antenna pattern performance of
the radiating element. As discussed above, the radiator unit 140
may be mounted more than a quarter wavelength in front of the
reflector 24. This may result in unbalanced currents flowing in the
coaxial feed cables 130-1, 130-2. In order to balance the currents,
a conductive stub 232 is used to physically and electrically
connect the outer conductors of the coaxial feed cables 130-1,
130-2. In some embodiments, the conductive stub 232 may comprise a
solder joint. In other embodiments, the conductive stub 232 may
comprise a conductive element that is soldered or otherwise
connected to the outer conductors of the coaxial feed cables 130-1,
130-2. In some embodiments, the conductive stub 232 may be
positioned about one quarter wavelength from the radiating unit
140.
FIGS. 5B and 5C illustrate the impact of the conductive stub 232 on
the antenna patterns of radiating element 200. The
"co-polarization" and "cross-polarization" antenna patterns are
shown in each graph, with the different curves representing the
performance at different frequencies across the operating frequency
band of radiating element 200. The co-polarization curves show the
power as a function of azimuth angle that is emitted by the
radiating element at the intended polarization. The
cross-polarization curves show the power as a function of azimuth
angle that is emitted by the radiating element at the other
polarization.
As shown in FIG. 5B, which depicts the simulated co-polarization
and cross-polarization azimuth patterns for the radiating element
200 if the conductive stub is not included, very high levels of
cross-polarized signal are present in the pattern at the two lowest
frequencies measured (both of which were near 1700 MHz). This level
of cross-polarized signal in the pattern is not acceptable. As
shown in FIG. 5C, which is a corresponding graph for radiating
element 200 when conductive stub 232 is included, the
cross-polarization levels are significantly reduced and acceptable
azimuth patterns are achieved.
FIGS. 5D and 5E illustrate the return loss as a function of
frequency for radiating element 200 without (FIG. 5D) and with
(FIG. 5E) the conductive stub 232 across the 1.695-2.690 GHz
operating frequency band of the radiating element. As shown in FIG.
5D, without conductive stub 232, unacceptably high levels of return
loss (more than -10 dB) are seen at the lower edge of the operating
frequency band. In contrast, FIG. 5E shows that when the conductive
stub 232 is added the return loss is below -13 dB across the entire
operating frequency band. FIG. 5F (without stub 232) and FIG. 5G
(with sub 232) show that adding the conductive stub 232 also
provides significant improvement in port-to-port isolation.
FIG. 6 is a rear perspective view of a radiating element 300
according to still further embodiments of the present invention
that includes a pair of metal tubes 336 that are mounted beside the
pair of coaxial feed cables 130-1, 130-2. The radiating element 300
may be identical to the radiating element 100 discussed above with
one exception, which is that two conductive tubes 336 are mounted
adjacent the outer conductors of the coaxial feed cables 130-1,
130-2. Note that various features of radiating element 300 are not
shown in FIG. 6, such as the stalk support 120 of the director unit
190. The tubes 336 may increase the port-to-port isolation of the
radiating element 300. The tubes 336 may be hollow metal tubes,
solid metal tubes or coaxial cables in example embodiments. The
addition of the tubes 336 balances the current on all four arms of
the radiating element 300.
FIG. 7 is a front view of a radiator unit 440 according to further
embodiments of the present invention. The radiator unit 440 can be
used, for example, in the radiating element 100 of FIGS. 2A-2B. As
shown in FIG. 7, the radiator unit 440 has an aspect ratio (defined
here as the ratio of width to height when the radiating element
including radiator unit 440 is mounted for normal use) that is less
than one. This occurs because both the conductive patch 450 and the
conductive ring 470 are elongated in the vertical direction.
By elongating the radiator unit 440 in the vertical direction, the
distance between adjacent elements in a column of radiating
elements may be reduced. This may help reduce the magnitude of
grating lobes, which refer to sidelobes in the elevation pattern
(and in particular at high elevation angles) that are in undesired
directions. The azimuth pattern for a radiating element that
includes radiator unit 440 may generally be the same as the azimuth
pattern for a radiating element that includes radiator unit 110,
while the beamwidth of the main lobe in the elevation pattern for
the radiating element that includes radiator unit 440 may be
reduced. The improvements in elevation beamwidth and grating lobe
reduction, however, have to be balanced against an expected
degradation in port-to-port isolation.
FIG. 8 is a front view of a radiator unit 540 according to still
further embodiments of the present invention. The radiator unit 540
is similar to the radiator unit 140 of FIG. 3A, but differs in that
the slots 552 extend all the way to the center of the conductive
patch 550, and the slots no longer extend to the periphery of the
conductive patch 550. The radiator unit 540 may generate similar
antenna patterns as those generated by radiator unit 140, and may
also exhibit similar return loss performance. One potential
difficulty with radiator unit 540 is that the center of the
conductive patch 550 is not metallized, and hence there is not a
convenient place to connect the coaxial feed cables 130-1, 130-2 to
the conductive patch 550, and the transmission lines of the feed
network that are in the center of the printed circuit board do not
have a ground plane on the opposite side of the dielectric.
Additionally, if the coaxial feed cables are mounted in the center
of the conductive patch 550, the outer conductors may negatively
impact the operation of the conductive patch 550. Thus, different
feed structures (not shown) such as feed cables may be used to feed
the slots 552 of conductive patch 550.
FIGS. 9A and 9B are a front view and a back view, respectively, of
a radiator unit 640 (which is implemented using a printed circuit
board 642) according to further embodiments of the present
invention, with the feed network of the radiator unit 640 omitted.
The radiator unit 640 includes a conductive patch 650 that is
implemented on two different metallization layers of the printed
circuit board 642. In particular, a first portion 651-1 of the
conductive patch 650 is implemented on a rear metallization layer
644 of the printed circuit board 642, while a second portion 651-2
of the conductive patch 650 is implemented on a front metallization
layer 646 of the printed circuit board 642. The first portion 651-1
comprises the central portion of the conductive patch 650 and has
four slots 652 therein while the second portion 651-2 comprises an
outer portion of the conductive patch 650 and has an annular shape
with the four slots 652 therein. The outer portion 651-2 overlaps
the central portion 651-1. In the depicted embodiment, plated
through holes 659 are used to electrically connect the two portions
651 of conductive patch 650 together. In other embodiments,
capacitive coupling may be used through the dielectric layer 648 of
printed circuit board 642.
A conductive ring 670 surrounds the outer portion 651-2 of the
conductive patch 650. The conductive ring 670 is formed on the
front metallization layer 646 of the printed circuit board 642 in
the depicted embodiment, although it may be formed on rear
metallization layer 644 in other embodiments. The feed network for
radiator unit 640, which is not shown in FIGS. 9A-9B to simplify
the drawings, may be identical (or at least substantially similar)
to the feed network 160 for radiator unit 140, and may be formed on
the front metallization layer 646 of printed circuit board 642 in
the interior of the annular second portion 651-2 of the conductive
patch 650.
FIGS. 10A and 10B are a front view and a back view, respectively,
of a radiator unit 740 (which is implemented using a printed
circuit board 742) according to still further embodiments of the
present invention, with the feed network omitted. The radiator unit
740 includes a conductive patch 750 that is implemented on two
different layers of the printed circuit board 742, but in this
case, the conductive patch 750 has three separate portions. The
first and third portions 751-1, 751-3 of the conductive patch 750
are implemented on a rear metallization layer 744 of the printed
circuit board 742, while the second portion 751-2 is implemented on
a front metallization layer 746 of the printed circuit board 742.
The first portion 751-1 comprises the central portion of the
conductive patch 750 and has four slots 752 therein, the second
portion comprises a middle portion 751-2 and has an annular shape
with four slots 752 therein, and the third portion comprises an
outer portion 751-3 and also has an annular shape with four slots
752 therein. The middle portion 751-2 overlaps both the central
portion 751-1 and the outer portion 751-3. In the depicted
embodiment, plated through holes 759 are used to electrically
connect the three portions 751 of conductive patch 750 together. In
other embodiments, capacitive coupling may be used through the
dielectric layer of the printed circuit board 742.
A conductive ring 770 surrounds the middle portion 751-2 of the
conductive patch 750. The conductive ring 770 is formed on the
front metallization layer 746 of the printed circuit board 742 in
the depicted embodiment, although it may be formed on rear
metallization layer 744 in other embodiments. The feed network for
radiator unit 740, which is not shown in FIGS. 10A-10B to simplify
the drawings, may be identical (or at least substantially similar)
to the feed network 160 for radiator unit 140, and may be formed on
the front metallization layer 746 of printed circuit board 742 in
the interior of the annular second portion 751-2 of the conductive
patch 750.
FIGS. 11A and 11B are a front view and a back view, respectively,
of a radiator unit 840 (which is implemented using a printed
circuit board) according to still further embodiments of the
present invention, with the feed network again omitted. Radiator
unit 840 is similar to radiator unit 140 discussed above, except
that adjacent arms 854 of radiator unit 840 are electrically
connected to each other by meandered traces 855 near the periphery
of the conductive patch 850. As a result, the conductive patch 850
includes a total of eight slots therein, namely four inner slots
852-1 through 852-4 and four outer slots 852-5 through 852-8. As
shown in FIG. 11B, on the front metallization layer 846 of the
printed circuit board, four metal pads 857 are provided that
overlap the meandered traces 855. As a result, the combination of a
meandered trace 855 and its corresponding overlapping metal pad 857
acts like a filtered connection between the two adjacent arms
854.
It will be appreciated that the above-described radiating elements
according to embodiments of the present invention may be combined
in any way to provide many additional embodiments. For example, the
conductive stub 232 of radiating element 200 and/or the conductive
tubes 336 of radiating element 300 may be included in any of the
other radiating elements described herein. Similarly, the
conductive ring structures of FIG. 4A or 4B may be used to replace
the conductive rings of any of the other embodiments, or the
conductive ring may be omitted in its entirety. Any of the radiator
units described herein may be elongated vertically like the
radiator unit 440 of FIG. 7, and/or the slot design for any of the
conductive patches may be modified to have the slot design of the
conductive patch 550 of FIG. 8. Additionally, any of the conductive
patches may be implemented as multi-layer conductive patches as
shown in FIGS. 9A-10B, or may include the filters that are provided
in the conductive patch 850 of FIGS. 11A-11B. All such embodiments
are considered to be within the scope of the present invention. It
will also be appreciated that this specification only describes a
few example embodiments, and that many changes may be made thereto
without departing from the scope of the present invention.
FIGS. 12A and 12B are front and rear views, respectively, of
another alternative radiator unit 940 that may be used in place of
the radiator unit 140 of the dual-polarized radiating element 100
of FIGS. 2A-2B. The radiator unit 940 may comprise a printed
circuit board 942 that has a first metallization layer 944 and a
second metallization layer 946 that are separated by a dielectric
layer 948. In the depicted embodiment, the first metallization
layer 944 is the rear metallization layer (FIG. 12B) and the second
metallization layer 946 is the front metallization layer (FIG.
12A).
Similar to the radiator unit 140 discussed above with reference to
FIG. 3A, the radiator unit 940 includes a conductive patch 950 that
is implemented in the rear metallization layer 944 of printed
circuit board 942. Four radial slots 952-1 through 952-4 are formed
in conductive patch 950, with each slot 952 extending outwardly
from near the center of the conductive patch 950. Each slot 952
comprises a region where the rear layer metallization is omitted
(or removed) to expose the dielectric layer 948 of printed circuit
board 942. Each slot 952 may be rotationally offset from adjacent
slots 952 by -90.degree. and 90.degree., respectively. As shown in
FIG. 12B, the four slots 952 divide the conductive patch 950 into
four arms 954-1 through 954-4. Each arm 954 of the conductive patch
950 has a generally T-shaped region where the metallization is
omitted to form respective openings 958, which extend inwardly from
the outer edge of the respective arms 954. The four arms 954
connect to each other in the central region of the conductive patch
950. A conductive ring 970 surrounds the conductive patch 950. The
conductive ring 970 is formed on the rear metallization layer 944
in the depicted embodiment, although it may be formed on front
metallization layer 944 in other embodiments. The conductive ring
970 may be identical to the conductive ring 170 of radiator unit
140. In other embodiments, part of the conductive ring 970 may be
formed in the front metallization layer 946 and the remainder may
be formed in the rear metallization layer 944.
The outer conductors of the two feed cables 130-1, 130-2 (FIGS.
2A-2B) may be soldered to the conductive patch 950 in the central
region of conductive patch 950. A ring-shaped (annular) solder mask
951 may be formed on the conductive patch 950 as shown in FIG. 12B.
The conductive patch 950 includes a pair of central openings 963
that receive the center conductors of the feed cables 130-1, 130-2
so that the center conductors may pass through the dielectric
substrate 948 to be electrically connected to a feed network 960
that is formed in the front metallization layer 946. The center
conductors of the two feed cables 130-1, 130-2 are electrically
isolated from the conductive patch 950.
Referring to FIG. 12A, the front metallization layer 946 of printed
circuit board 942 includes the feed network 960, which is used to
couple RF signals to and from the conductive patch 950. The feed
network 960 may be similar to or identical to the feed network 160
discussed above with reference to FIG. 3A, and hence further
description thereof will be omitted here. A solder mask 962 may be
formed on the central region of the feed network 960 to facilitate
soldering the central conductors of the feed cables 130-1, 130-2 to
the inputs of the feed network 960. As is shown in FIG. 12A, the
front metallization layer 946 may further include four conductive
plates 959 that together form a broken annular ring. The broken
annular ring may generally surround the feed network 960. Each
conductive plate 959 may overlap a respective one of the T-shaped
openings 958 in the arms 954 of the conductive patch 950. The
conductive plates 959 may capacitively couple with the underlying
conductive patch 950.
FIGS. 13A and 13B are shadow front and back views, respectively, of
the radiator unit printed circuit board 942 of FIGS. 12A and 12B.
The solder masks 951, 962 that are shown in the middle of FIGS.
12A-12B are omitted in FIGS. 13A-13B to better illustrate the rear
and front metallization layers 944, 946.
The radiator unit 940 of FIGS. 12A-13B may have the general design
of the radiator unit disclosed in FIGS. 7-8of U.S. Pat. No.
7,688,271. In particular, referring to FIGS. 13A-13B, it can be
seen that each arm 954 of conductive patch 950 includes a first
half 954A and a second half 954B that comprise respective first and
second legs 954A, 954B that extend radially outwardly from the
central region of the printed circuit board 942. Each pair of a
first leg 954A of a first arm 954 and an adjacent second leg 954B
of an adjacent second arm 954 together form a generally T-shaped
dipole radiator 953, as can be seen in the dashed box in FIG. 13B.
Each slot 952 separates the first and second legs 954A, 954B of a
respective one of the dipole radiators 953. The four dipole
radiators 953 form a dipole square that has a generally octagonal
profile. As with the radiator unit disclosed in FIGS. 7-8 of U.S.
Pat. No. 7,688,271, each dipole radiator 953 is fed by a respective
hook shaped feed line 966 that crosses the respective slot 952 of
the dipole radiator 953 on the opposite side of the printed circuit
board 942.
There are several differences between the radiator unit disclosed
in FIGS. 7-8 of U.S. Pat. No. 7,688,271 and the radiator unit 940
of FIGS. 12A-13B. For example, in radiator unit 940, the feed
network 960 is implemented on the front metallization layer 946 and
the dipole radiators 953 are implemented on the rear metallization
layer 944, which is the reverse of what is shown in U.S. Pat. No.
7,688,271. As another example, in U.S. Pat. No. 7,688,271 the
openings in each arm of the conductive patch where the
metallization is removed are generally diamond-shaped as compared
to the generally T-shaped openings 958 included in the arms 954 of
radiator unit 940. As another example, the radiator unit 940
includes the conductive plates 959 that are formed on the front
metallization layer 944, which are not provided in the radiator
unit of U.S. Pat. No. 7,688,271. Additionally, U.S. Pat. No.
7,688,271 uses a printed circuit board-based feed stalk to feed the
RF signals to and from the radiator unit thereof, while the
radiator unit 940 is designed to be fed directly by a pair of
coaxial cables 130-1, 130-2.
Pursuant to further embodiments of the present invention,
techniques for grounding radiating elements are provided that may
be used to suppress a common mode resonance that may distort the
radiation pattern of nearby radiating elements that operate in a
different frequency band. These techniques may be used, for
example, with any of the radiating elements according to
embodiments of the present invention that are disclosed herein. As
described above, coaxial feed cables may be used as the feed
elements for the radiating elements according to embodiments of the
present invention. As is also described above, in some embodiments,
the outer conductors of the coaxial feed cables 130 may not be
coupled to the reflector 24 underneath the radiating elements, but
instead may be coupled to the reflector 24 elsewhere within the
antenna. As a result, the outer conductors of the coaxial feed
cables 130 may appear as a monopole element that has a length equal
to the distance from where the outer conductor of each coaxial feed
cable 130 is grounded to the reflector 24 at the point where the
coaxial feed cable 130 connects to one of the radiator units (e.g.,
radiator unit 140) according to embodiments of the present
invention. If the monopole element formed by the outer conductor of
a coaxial feed cable 130 has a length that is resonant within an
operating frequency band of other radiating elements that may be
included in the base station antenna, then the coaxial feed cables
130 may generate common mode resonances in the response of these
other radiating elements, degrading the performance thereof.
Pursuant to embodiments of the present invention, the points where
the outer conductors of the coaxial feed cables 130 for a radiating
element are coupled to a common ground reference such as the
reflector of an antenna may be selected so that common mode
resonances will not be generated in the response of other radiating
elements included in the antenna. In particular, the length of the
"monopole" segment of each coaxial feed cable that extends from the
radiator unit that the coaxial feed cable 130 feeds to the point
where the coaxial feed cable 130 is connected to a common ground
reference (e.g., the reflector 24) may be set to be a length that
will not resonate in the operating frequency band of any other
nearby radiating elements. Thus, for example, if the coaxial feed
cables are used to feed so-called high band radiating elements that
operate in the 1,695-2,690 MHz frequency band that are mounted
adjacent other so-called low-band radiating elements that operate
in the 696-960 MHz frequency band, then the lengths of the
above-described "monopole" segments of the coaxial feed cables 130
will be selected so that they are not resonant in the 696-960 MHz
frequency band (e.g., the lengths of the monopole segments will not
be equal to a quarter wavelength, a half, wavelength, three
quarters of a wavelength, one wavelength, etc. for any frequency
within the 696-960 MHz frequency band). This technique may be used
to suppress a common mode resonance that otherwise could degrade
the performance of the low band radiating elements.
FIG. 14A is a side view of a portion of a base station antenna that
includes a pair of radiating elements mounted on a reflector that
are fed by a power divider printed circuit board that is mounted
behind the reflector. FIG. 14B is a rear view of the power divider
printed circuit board of FIG. 14A. FIGS. 14A and 14B will be used
to explain how the above-described common mode resonances can be
suppressed in nearby radiating elements that operte in different
frequency bands.
As shown in FIG. 14A, the base station antenna includes a reflector
1000 and first and second radiating elements 1010-1, 1010-2 that
are mounted to extend forwardly from the reflector 1000. The first
radiating element 1010-1 is fed by a first pair of coaxial feed
cables 1030-1, 1030-2. The second radiating element 1010-2 is fed
by a second pair of coaxial feed cables 1030-3, 1030-4. A power
divider printed circuit board 1050 is mounted on the rear side of
the reflector 1000.
As shown in FIG. 14B, the power divider printed circuit board 1050
includes first and second input ports 1052-1, 1052-2, and first
through fourth output ports 1054-1 through 1054-4. First and second
input coaxial cables 1060-1, 1060-2 are coupled to the respective
first and second input ports 1052-1, 1052-2. The coaxial feed
cables 1030-1, 1030-2 for the first radiating element 1010-1 are
coupled to the respective first and second output ports 1054-1,
1054-2. The coaxial feed cables 1030-3, 1030-4 for the second
radiating element 1010-2 are coupled to the respective third and
fourth output ports 1054-1, 1054-2. The power divider printed
circuit board 1050 may include transmission lines 1056 such as, for
example, microstrip transmission lines and a pair of power divider
circuits such as, for example, Wilkinson power dividers 1058. A
first transmission line 1056-1 may connect the first input port
1052-1 to an input of the first power divider circuit 1058-1 and
third and fourth transmission lines 1056-3, 1056-4 may connect the
first and second outputs of the first power divider circuit 1058-1
to the respective first and second output ports 1054-1, 1054-2.
Similarly, a second transmission line 1056-2 may connect the second
input port 1052-2 to an input of the second power divider circuit
1058-2 and fifth and sixth transmission lines 1056-5, 1056-6 may
connect the first and second outputs of the second power divider
circuit 1058-2 to the respective third and fourth output ports
1054-3, 1054-4.
As is further shown in FIG. 14B, the power divider printed circuit
board 1050 may include one or more grounding tabs 1059 where a
ground reference for the transmission lines 1056 is coupled to the
reflector 1000. The grounding tabs 1059 may comprise an electrical
connection (which may be a galvanic connection or a capacitive
connection, for example) between the ground reference for the
transmission lines 1056 and the reflector 1000.
As shown in FIG. 14A, a first segment 1032 of each coaxial feed
cable 1030 extends forwardly from the reflector 1000 to the
radiator unit 1040 of its associated radiating element 1010. The
length of each first segment 1032 may be L1, which is typically
between a quarter wavelength and three-eighths of a wavelength of
the center frequency of the operating frequency band of the
radiating element 1010. These segments 1032 may appear as monopoles
that extend forwardly from the reflector/ground plane 1000. Each
coaxial feed cable 1030 includes a second segment 1034 that extends
along the back side the reflector 1000 from the distal end of the
first segment 1032 to the power divider printed circuit board 1050.
The length of each second segment 1034 may be L2, and the length L2
may be selected by an antenna designed based on the location of the
power divider printed circuit board 1050. As shown in FIG. 14B,
each output port 1054 on power divider printed circuit board 1050
may be located a distance L3 from the closest ground tab 1059 (note
that the distance L3 may be different for each output port
1054).
RF energy emitted by another radiating element 1070 that operates
in a different frequency band may be present in the vicinity of the
first segments 1032 of the coaxial feed cables 1030. As noted
above, the first segments 1032 of the coaxial feed cables 1030 may
appear as monopole elements that extend forwardly from the
reflector 1000. Moreover, since each coaxial feed cable 1030 has a
ground connection to the reflector 1000 at one of the grounding
tabs 1059, the effective length of these monopole elements is not
the length L1 of the first segments 1032 that extend forwardly from
the reflector 1000, but instead is the sum of L1+L2+L3 for each
coaxial feed cable 1030. If this effective length is a length that
is resonant within the operating frequency band of the radiating
element 1070, then the RF energy emitted by radiating element 1070
may induce currents on the coaxial feed cables 1030, generating the
common mode resonance in the frequency response of the radiating
element 1070. This common mode resonance will occur in a relatively
tight range of frequencies for which the effective length of the
monopole element is resonant within the operating frequency band of
radiating element 1070. Unfortunately, this common mode resonance
can degrade the performance of radiating element 1070.
An antenna designer may select the distance L2 based on the
location of the power divider printed circuit board 1050 with
respect to the radiating elements 1010, and may select the distance
L3 based on the size of the power divider printed circuit board and
the locations of the grounding tabs 1059 and the output ports 1054.
As such, the antenna designer can select the effective length of
the monopole element formed by each coaxial feed cable 1030. By
selecting these effective lengths to not be lengths where the
monopole elements will be resonant in the operating frequency
band(s) of other nearby radiating elements, the generation of a
common mode resonance in the response of the nearby radiating
elements may be suppressed.
While FIGS. 14A and 14B illustrate an example where the radiating
elements 1010-1, 1010-2 are fed through a power divider printed
circuit board 1050, it will be appreciated that embodiments of the
present invention are not limited thereto. For example, in other
embodiments, the coaxial feed cables 1030 may connect to a phase
shifter or other circuit element that may or may not include a
grounding tab. Moreover, if a grounding tab is not provided, the
coaxial feed cables may be grounded to the reflector in other ways.
For example, a small portion of the cable jacket of each coaxial
feed cable 1030 may be removed and the outer conductor of each
coaxial feed cable 1030 that is exposed through the opening in the
cable jacket may be soldered to the reflector 1000 to provide the
ground reference. When this approach is taken, the effective length
of each monopole element may be L1+L2, where L2 is the length of
the second cable segment 1034 that extends between cable segment
1032 and the point where the coaxial feed cable 1030 is soldered to
the reflector 1000.
The radiating elements discussed above have primarily been
implemented using radiator unit printed circuit boards having two
metal layers, with a conductive patch of the radiating element
implemented at least primarily on one metal layer and the feed
network implemented primarily on the other layer of the printed
circuit board. Embodiments of the present invention, however, are
not limited thereto. For example, FIGS. 15A-15D illustrate a
radiating element 1100 according to further embodiments of the
present invention that is implemented primarily from sheet metal.
Sheet metal radiating elements may be cheaper than corresponding
printed circuit board based radiating elements, and allow for
three-dimensional radiator units that may have a smaller size or
"footprint" on the reflector of the antenna. This smaller footprint
may allow an array formed of the radiating elements to be
positioned closer to other arrays of radiating elements, allowing
for a reduction in the size of an antenna including these radiating
elements and/or the inclusion of more arrays in the antenna.
Referring first to FIGS. 15A-15B, FIG. 15A is a side view of the
sheet metal based radiating element 1100, while FIG. 15B is a
schematic view of a lower portion of one of the metal plates of the
feed stalk of the radiating element of FIG. 15A illustrating how a
feed line may be mounted thereon to form a microstrip feed
line.
As shown in FIGS. 15A-15B, the radiating element 1100 includes a
feed stalk 1110 and a radiator unit 1140. The feed stalk 1110 is
used to mount the radiator unit 1140 forwardly of the reflector
(not shown) of a base station antenna. The feed stalk 1110 includes
an L-shaped metal stalk 1120 and a pair of traces 1132-1, 1132-2.
It will be appreciated that the metal feed stalk 1120 may have
other shapes (cross-sections) such as, for example, square shape,
triangular shape, cruciform shape, etc. Each trace 1132 is part of
a larger feed structure 1130, as will be discussed below. The
L-shaped metal stalk 1120 includes first and second metal plates
1122-1, 1122-2, which may comprise a single piece of metal that is
bent at a 90.degree. angle to define the two plates 1122-1, 1122-2.
The first trace 1132-1 is mounted on the first metal plate 1122-1
and the second trace 1132-2 is mounted on the second metal plate
1122-2 so as to form first and second microstrip transmission lines
1124-1, 1124-2, with the metal plates 1122 serving as the ground
conductors of the microstrip transmission lines 1124 and the traces
1132 serving as the signal traces of the respective microstrip
transmission lines 1124.
As shown in FIG. 15B, the traces 1132 may be mounted on the
respective metal plates 1122 using, for example, dielectric
stand-off rivets 1126 that mount each trace 1132 at a predetermined
distance from its associated metal plate 1122, where the
predetermined distance may be selected so that the microstrip
transmission lines 1124 may have a desired impedance. The traces
1132 may have features 1134 such as widened areas and or openings
that mate with the dielectric stand-off rivets 1126 that facilitate
mounting the traces 1132 to the metal plates 1122 and maintaining
the desired impedance. As shown in FIG. 15B, a rear portion of each
metal plate 1122 may be bent at a 90.degree. angle (other angles
may be used; preferably an angle of at least 30.degree. is used to
obtain a significant reduction in the size of the radiating
element) to form a tab 1128 that facilitates mounting the metal
stalk 1120 to extend forwardly from a reflector 24 using dielectric
rivets 1127. A dielectric pad 25 may be interposed between the
reflector 24 and the tab 1128. Alternatively, metal rivets may be
used and the dielectric pad 25 may be omitted to provide a galvanic
connection instead of a capacitive connection between the metal
stalk 1120 and the reflector 24. First and second coaxial feed
cables (not shown) may be electrically coupled to the microstrip
transmission lines 1124. For example, the outer (ground) conductor
of each coaxial feed cable may be soldered to the reflector 24 and
capacitively coupled to the metal stalk 1120 through the dielectric
pads 25, and the traces 1132 may extend rearwardly through openings
26 in the reflector 24 so that the inner conductors of the
respective first and second coaxial feed cables may be soldered to
the rear end of each trace 1132 behind the reflector 24. The first
and second coaxial feed cables may connect the radiating element
1100 to another component of a base station antenna such as an
electromechanical phase shifter assembly or a power divider.
While the feed stalk 1110 of FIGS. 15A-15B comprises a metal stalk
1120 and a pair of traces 1132-1, 1132-2, it will be appreciated
that in other embodiments other types of feed stalks may be used
such as, for example, coaxial feed cables, printed circuit board
feeds, etc.).
FIGS. 15C and 15D are a front perspective shadow and a front shadow
view, respectively, of a radiator unit 1140 of the radiating
element 1100 of FIG. 15A. Referring to FIGS. 15C-15D, the radiator
unit 1140 may be mounted on a forward end of metal stalk 1120 via,
for example, soldering. The radiator unit 1140 may be implemented
using pieces of stamped sheet metal and four small printed circuit
boards. A first piece of sheet metal 1142 may form a conductive
patch 1150. The first piece of sheet metal 1142 may have a square
shape and may be formed by stamping the square piece of sheet metal
1142 to form a plurality of slots 1152, 1154 therein, and then
bending the four outer edges 1156 of the piece of sheet metal 1142
upward at an angle of about 90.degree. (FIGS. 15A and 15C). The
four outer edges 1156 may be bent downwardly in other embodiments,
or some of the outer edges 1156 may be bent upwardly and others
downwardly. The outer edges 1156 may each be bent at an angle of at
least 30.degree., or at an angle of at least 45.degree., or at an
angle of at least 60.degree.. In some embodiments, the outer edges
1156 may each be bent at an angle of approximately 90.degree. with
respect to the inner portions of the arms 1154. Slots 1152-1
through 1152-4 extend radially from a respective point near the
center of the first piece of sheet metal 1142 to the periphery of
the conductive patch 1150. Each of the first through fourth slots
1152-1 through 1152-4 includes a first portion that extends in a
plane defined by an inner portion (the central region) of the
conductive patch 1150, and a second portion that extends at an
oblique angle with respect to the first portion. Each slot 1152 may
be rotationally offset from adjacent slots by -90.degree. and
90.degree., respectively. The slots 1152 extend through the
upwardly bent outer edges 1156 of the square piece of sheet metal
1142, and hence each slot 1152 extends to the periphery of the
conductive patch 1150.
The first and second slots 1152-1, 1152-2 may extend along a first
common plane and the third and fourth slots 1152-3, 1152-4 may
extend along a second common plane that is perpendicular to the
first common plane. Each of the slots 1152 may extend from a
periphery of the conductive patch 1150 towards the middle or
"central region" of the conductive patch 1150, and the four slots
1152 may divide the conductive patch 1150 into the four arms 1154-1
through 1154-4. The four arms 1154 are electrically connected to
each other in a central region of the conductive patch 1150 and
extend outwardly from the central region of the conductive patch
1150.
Openings in the form of slots 1158-1 through 1158-4 are formed in
the respective upwardly bent outer edges 1156 of the square piece
of sheet metal 1142. Thus, a slot 1158 is formed in each arm 1154.
The slots 1158 may be generally T-shaped slots in some embodiments,
as shown. Each slot 1158 may extend to a distal portion of a
respective arm 1154. Four small printed circuit boards 1144 are
provided. Each printed circuit board 1144 includes a dielectric
substrate (not shown) that directly contacts a respective one of
the upwardly bent outer edges 1156 of the square piece of sheet
metal 1142, and a metal layer formed on the outer side of
dielectric substrate. Each printed circuit board 1144 overlaps a
respective one of the upwardly bent outer edges of the square piece
of sheet metal 1142. The printed circuit boards 1144 may be
attached to the upwardly bent outer edges 1156 of the square piece
of sheet metal 1142 be any appropriate fashion including, for
example, adhesives, double-sided tapes, rivets, screws or other
fasteners. Each printed circuit board 1144 may cover a respective
one of the slots 1158. In other embodiments, the printed circuit
boards 1144 may be replaced with metal sheets that may be attached
to the upwardly bent outer edges 1156 of the square piece of sheet
metal 1142 via adhesive tape or other means that allow the metal
sheets to capacitively couple to the upwardly bent outer edges 1156
of the square piece of sheet metal 1142. Each metal layer (whether
in the form of a metal layer on a printed circuit board 1144 or a
metal sheet) may capacitively couple with the outer edge 1156 of a
respective one of the arms 1154.
As noted above, the traces 1132-1, 1132-2 are each part of a
respective feed structure 1130-1, 1130-2. Each feed structure
1130-1, 1130-2 may comprise a monolithic piece of stamped and bent
sheet metal. Feed structure 1130-1 includes first and second feed
lines 1166-1, 1166-2, while feed structure 1130-2 includes third
and fourth feed lines 1166-3, 1166-4. Thus, the first and second
feed lines 1166-1, 1166-2 are physically and electrically connected
to the first trace 1132-1, and the third and fourth feed lines
1166-3, 1166-4 are electrically connected to the second trace
1132-2.
Feed line 1166-1 crosses the first slot 1152-1 and feed line 1166-2
crosses the second slot 1152-2. Accordingly, RF signals that are
incident on the first trace 1132-1 split so that a portion of the
RF energy passes to each of the first and second feed lines 1166-1,
1166-2. Feed line 1166-3 crosses the third slot 1152-3 and feed
line 1166-4 crosses the fourth slot 1152-4. Thus, RF signals that
are incident on the second trace 1132-2 split so that a portion of
the RF energy passes to each of the third and fourth feed lines
1166-3, 1166-4. The RF energy passes along each feed line 1166 to
cross a respective one of the slots 1152. Each feed line 1166
terminates into a respective one of four quarter wavelength stubs
1168. As a result, RF signals that are input on feed lines 1166-1
through 1166-4 feed the respective slots 1152-1 through 1152-4,
causing the conductive patch 1150 to radiate RF energy.
The first and second feed lines 1166-1, 1166-2 are positioned
forwardly of the conductive patch 1150, as can best be seen in FIG.
15A. The third and fourth feed lines 1166-3, 1166-4 are positioned
rearward of the conductive patch 1150. A pair of dielectric spacers
(not shown) are provided, the first of which is interposed between
the first and second feed lines 1166-1, 1166-2 and the conductive
patch 1150, and the second of which is interposed between the third
and fourth feed lines 1166-3, 1166-4 and the conductive patch 1150.
The dielectric spacers may physically and electrically separate the
first and second feed structures 1130-1, 1130-2 from the first
piece of metal 1142. Each feed line 1166 may comprise an air
microstrip transmission line. In other embodiments, the feed lines
1166 may comprise conventional microstrip transmission lines.
It will be appreciated that many modifications may be made to the
radiating element 1100 of FIGS. 15A-15D. For example, FIG. 15E is a
front shadow view of a modified version of a radiator unit 1140'
that may be used in place of the radiator unit 1140 in the
radiating element 1100. The radiator unit 1140' may be identical to
the radiator unit 1140 of FIGS. 15C-15D except that the outer edges
1156 of radiator unit 1140' are not bent upwardly or downwardly so
that the conductive patch 1150 is a planar element.
FIGS. 15F and 15G are a front perspective shadow view and a front
shadow view, respectively, of another modified version 1140'' of
the radiator unit of FIGS. 15C-15D. As shown in FIGS. 15F and 15G,
the radiator unit 1140'' is identical to the radiator unit 1140
except that the base of the T-shaped slots 1158 is extended so that
the slots 1158 extend farther into the interior of the conductive
patch 1150.
Notably, positioning the first and second feed lines 1166-1, 1166-2
on one side of the conductive patch 1150 while positioning the
third and fourth feed lines 1166-3, 1166-4 on the other side of the
conductive patch 1150 eliminates any need to provide special
structures to prevent conductive lines 1166-1 and 1166-3 from
electrically short-circuiting at the location where they "cross"
when viewed from the front. However, it will be understood that all
of the feed lines 1166 may be implemented on the same side (either
front or back) of the conductive patch 1150 in other embodiments,
as shown above with respect to other radiating elements according
to embodiments of the present invention.
While monolithic sheet metal feed structures 1130-1, 1130-2 are
used in the depicted embodiment, it will be appreciated that in
other embodiments the first and second feed lines 1166-1, 1166-2
may be implemented using a first printed circuit board, and that
the third and fourth feed lines 1166-3, 1166-4 may be implemented
using a second printed circuit board. The traces 1132-1, 1132-2 may
be electrically coupled to the respective printed circuit boards.
If printed circuit boards are used, the feed branches may be
implemented as coplanar waveguide or grounded coplanar waveguide
transmission lines in the same manner discussed above with other
embodiments of the present invention.
Bending the outer edges of the first piece of stamped metal 1142
may reduce the "footprint" of the radiating element 1100 (i.e., the
area of the radiating element 1100 when viewed from the front).
This may allow an array of radiating elements 1100 included in an
antenna to be positioned closer to other arrays. As the radiating
element 1100 may be formed primarily of stamped sheet metal it may
be cheaper to fabricate than comparable radiating elements formed
using printed circuit boards.
Embodiments of the present invention have been described above with
reference to the accompanying drawings, in which embodiments of the
invention are shown. This invention may, however, be embodied in
many different forms and should not be construed as limited to the
embodiments set forth herein. Rather, these embodiments are
provided so that this disclosure will be thorough and complete, and
will fully convey the scope of the invention to those skilled in
the art. Like numbers refer to like elements throughout.
It will be understood that, although the terms first, second, etc.
may be used herein to describe various elements, these elements
should not be limited by these terms. These terms are only used to
distinguish one element from another. For example, a first element
could be termed a second element, and, similarly, a second element
could be termed a first element, without departing from the scope
of the present invention. As used herein, the term "and/or"
includes any and all combinations of one or more of the associated
listed items.
It will be understood that when an element is referred to as being
"on" another element, it can be directly on the other element or
intervening elements may also be present. In contrast, when an
element is referred to as being "directly on" another element,
there are no intervening elements present. It will also be
understood that when an element is referred to as being "connected"
or "coupled" to another element, it can be directly connected or
coupled to the other element or intervening elements may be
present. In contrast, when an element is referred to as being
"directly connected" or "directly coupled" to another element,
there are no intervening elements present. Other words used to
describe the relationship between elements should be interpreted in
a like fashion (i.e., "between" versus "directly between",
"adjacent" versus "directly adjacent", etc.).
Relative terms such as "below" or "above" or "upper" or "lower" or
"horizontal" or "vertical" may be used herein to describe a
relationship of one element, layer or region to another element,
layer or region as illustrated in the figures. It will be
understood that these terms are intended to encompass different
orientations of the device in addition to the orientation depicted
in the figures.
The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" "comprising," "includes" and/or
"including" when used herein, specify the presence of stated
features, operations, elements, and/or components, but do not
preclude the presence or addition of one or more other features,
operations, elements, components, and/or groups thereof.
Aspects and elements of all of the embodiments disclosed above can
be combined in any way and/or combination with aspects or elements
of other embodiments to provide a plurality of additional
embodiments.
* * * * *